Cleaning of lubricating oils for diesel engines on board ships or in diesel power stations may involve problems since contaminants have a very low density, have a small particle size and are usually kept in suspension within the oil by detergent and dispersant additives present in the lubricating oil.
Conventional separation and filter technologies may remove larger contaminants but the smaller particles are usually harder to remove. This means that oil in use in the diesel engine is often contaminated with combustion residues such as soot, inorganic reaction residues such as calcium sulphate from sulphuric acid and alkaline additives. Further, the typical concentration of pentane is about 0.5-1% in the used oil. The high amount of insoluble increases the viscosity of the lubricating oil and thereby reduces the lubricating and cleaning properties.